0 4.3BSD; This option is primarily used to build root file systems that can be understood by older boot ROMs. This generates an FFSv1 file system with level 1 format.
1 FFSv1; normal Fast File System, level 4 format. Also known as `FFS', `UFS', or `UFS1'. This is the default.
2 FFSv2; enhanced Fast File System, suited for more than 1 Terabyte capacity. This is also known as `UFS2'.